This invention relates generally to new and improved apparatus and process for piercing a workpiece such as a billet or rod; more particularly this invention relates to new and improved apparatus and process for providing forced lubrication between a piercing punch and a workpiece to reduce friction therebetween during piercing, and also for providing such forced lubrication piercing for causing self-centering of the piercing punch with respect to the workpiece during piercing.
Cold and hot piercing are well known to those skilled in the metal working art. However, as is also known to the art both cold and hot piercing prior art techniques have undesirable characteristics. Due to the high friction that develops between the piercing punch and the billet or rod being pierced, cold piercing is generally limited to relatively small diameter and short length piercing. Large diameter and longer length piercing may be accomplished by heating the billet or rod to, or substantially to, its plastic state whereby the friction and force required in hot piercing is reduced. Such hot piercing, as is also known to those skilled in the art, due to the heating requirement is undesirably expensive and complicated. Further, while cold piercing can produce final product, final product typically cannot be produced by hot piercing because upon cooling the pierced metal shrinks, suffers surface degradation, etc., which requires undesirable post hot piercing finishing steps.
Centering of the piercing punch with respect to the rod or billet during piercing is another well known prior art problem associated with piercing.
Accordingly, there exists a need in the piercing art for new and improved piercing process and apparatus for overcoming the above-noted piercing problems attendant to prior art piercing, which permits larger diameter cold piercing of final product to be achieved and which also provides self-centering.